Endothelin-2 signaling in the neural retina promotes the endothelial tip cell state and inhibits angiogenesis

Abstract

Endothelin signaling is required for neural crest migration and homeostatic regulation of blood pressure. Here, we report that constitutive overexpression of Endothelin-2 (Edn2) in the mouse retina perturbs vascular development by inhibiting endothelial cell migration across the retinal surface and subsequent endothelial cell invasion into the retina. Developing endothelial cells exist in one of two states: tip cells at the growing front and stalk cells in the vascular plexus behind the front. This division of endothelial cell states is one of the central organizing principles of angiogenesis. In the developing retina, Edn2 overexpression leads to overproduction of endothelial tip cells by both morphologic and molecular criteria. Spatially localized overexpression of Edn2 produces a correspondingly localized endothelial response. Edn2 overexpression in the early embryo inhibits vascular development at midgestation, but Edn2 overexpression in developing skin and brain has no discernible effect on vascular structure. Inhibition of retinal angiogenesis by Edn2 requires expression of Endothelin receptor A but not Endothelin receptor B in the neural retina. Taken together, these observations imply that the neural retina responds to Edn2 by synthesizing one or more factors that promote the endothelial tip cell state and inhibit angiogenesis. The response to Edn2 is sufficiently potent that it overrides the activities of other homeostatic regulators of angiogenesis, such as Vegf.

Activation of the Endothelin System Mediates Pathological Angiogenesis during Ischemic Retinopathy

“…Consequently, this leads to inhibition of physiological angiogenesis, localized increases in vascular sprouting, and overgrowth of hypoxic, misguided, and nonperfused vessels. 22 Such vessels are morphologically similar to NV tufts observed during pathological angiogenesis. We find that in a disease model, ischemiainduced endothelin system activation via EDNRA leads to increased production of VEGFA protein and ANGPT2, DLL4, APLN, and CCL2 transcripts.…”

“…Moreover, EDN2-dependent inhibition of angiogenesis in the neural retina is mediated through EDNRA, but not EDNRB. 22 These data suggest that EDN2 activation of EDNRA plays a significant role in inhibiting angiogenesis in the developing retina. However, the impact of ETs and their receptors on pathological NV in ischemic retinopathy is completely unknown.…”

“…35 In isolated porcine retinal arterioles, EDN1 stimulation causes vasoconstriction through the activation of EDNRA, suggesting that endothelins also play a significant role in maintaining retinal homeostasis. 39 A recent study by Rattner et al 22 suggests that overexpression of EDN2 in the neural retina provokes hypoxia and inhibits developmental angiogenesis via activation of EDNRA and not EDNRB. To our knowledge, our studies provide the first evidence of endothelin system activation during ischemic retinopathy and that pathological angiogenesis is reduced predominantly through inhibition of EDNRA, and not EDNRB, further extending previous findings.…”

“…Rattner et al 22 recently showed that EDN2 acting on EDNRA, but not EDNRB, on retinal neurons and/or glia induces hypoxia and production of one or more factors that arrest migration of the developing vasculature. Their studies suggest that paracrine or autocrine signaling of endothelins must limit their diffusion and that local action of endothelins must take place in the close proximity with retinal neurons and ECs.…”

The Role of the Hypoxia Response in Shaping Retinal Vascular * Development in the Absence of Norrin/Frizzled4 Signaling

“…28. Within each figure, retinal sections from mice with different genotypes that were subjected to VEGF in situ hybridization were processed in parallel and imaged with identical settings.…”